Victoria in July 2009:

Warm and dry conditions continue.

Note that Melbourne's rainfall total for the year thus far is 165.4 mm, the lowest January to July total since 1976 (when 159.9 mm fell).

Preliminary data for July 2009 shows that the relatively warm and relatively dry conditions, that have been a feature of the weather over recent times (refer to the Table below for Melbourne average conditions prior to, and since the start of, the current decade), continues.

Both overnight and daytime temperatures during the month averaged between half a degree and one degree above long-term normals throughout the State, whilst rainfall was somewhat below normal in most districts - the exceptions were the southwest and about the ranges.

The reason for the mostly drier conditions (than usual) during the month relates to a high frequency of westerly or northwesterly synoptic types which, for the most part, were relatively benign (in that they were not accompanied with northwest cloud bands, which normally bring Victoria quite a deal of rainfall ahead of cold fronts).

The reason for the mostly warmer conditions (than usual) during the month relates to the almost a complete absence of southwesterly or southerly synoptic types, which usually bring "cold outbreaks" to Victoria, accompanied by snowfalls on the ranges down to low levels, and followed by spells of frosty nights once the weather clears.

Specifically for Melbourne for the month thus far:

- Only 39.6 mm of rain has fallen (compared to the average over all years of record of 46.2 mm; the average for July 1855−1999 of 48.2 mm; and, the average for July since 2000 of 39.8 mm),

- The average minimum temperature has been 8.2°C(compared to the average over all years of record of 5.9°C; the average for July 1855−1999 of 5.9°C; and, the average for July since 2000 of 7.5°C); and,

- The average maximum temperature has been 15.2°C(compared to the average over all years of record of 13.5°C; the average for July 1855−1999 of 13.4°C; and, the average for July since 2000 of 14.6°C).

You may wish to refer to the Table below for Melbourne average conditions prior to, and since the start of, the current decade.

The decline in rainfall may be explained in terms of a
poleward retreat of rain-bearing mid-latitude depressions.

The rise in temperature is consistent with warming that has been observed in cities in other parts of the world.

The greater warming at night is due to the "heat island effect" (whereby major cities have been observed to have warmed more, especially at night, than their forested and grassed surroundings, on account of the roads, concrete, and buildings).

Long-Term Climate Averages

Notes

This statement has been prepared based on information available at
3 pm on Monday 3 August 2009.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

Averages are long-term means based on observations from
all available years of record, which vary widely from site to site.
They are not shown for sites with less than 10 years of record, as they cannot then be calculated reliably.
The median
is sometimes more representative than the
mean
of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
decile ranking
(very low rainfall is in decile 1, low in decile 2 or 3,
average in decile 4 to 7, high in decile 8 or 9
and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a
percentage of the long-term mean.